Publication Abstract

The ovulatory cycle and a method to determine the stage of spawning in cod, Gadus morhua

O.S. Kjesbu, P.R. Witthames, P. Solemdal, M. Greer-Walker and P. Bratland

The size frequency distribution of the vitellogenic oocytes in Atlantic cod (Gadus morhua) changes in a predictable manner as spawning progresses. This change was studied by sampling successive batches of eggs from reared cod kept in the laboratory. The shape of the vitellogenic oocyte mode was described by measuring the diameter, standard deviation, and skewness and kurtosis. Linear regressions were derived which related the portion of the total number of eggs spawned per season (PES) to the number of vitellogenic oocytes per gram of the ovary and in relation to the standard deviation of the distribution. A detailed description is given of the oocyte growth during ovulatory rhythm. The rhythm consists of four periods: arrest, final growth, hydration, and ovulation. It is suggested that the egg size is determined during the final growth period.

Reference:

O.S. Kjesbu, P.R. Witthames, P. Solemdal, M. Greer-Walker and P. Bratland, (1990). The ovulatory cycle and a method to determine the stage of spawning in cod, Gadus morhua. Canadian Journal of Fisheries and Aquatic Sciences, 47(6): 1185-1193.